This invention relates to electromagnetic projectile launchers and more particularly to such launchers which utilize projectile launching rails having controlled cross-sectional shapes to improve projectile accelerating forces.
In a parallel rail electromagnetic launcher, a force accelerates a current carrying conductor in a magnetic field and this force is equal to the vector cross product of the current density and the magnetic flux density. It can be shown that this force is equal to 1/2 L'I.sup.2 where L' is the inductance gradient of the parallel rail configuration and I is the current. Since the magnetic field which interacts with and therefore accelerates a current carrying conducting armature or plasma is primarily produced by the conducting rails just in the wake of the armature, for example, the field produced by the time dependent current distribution which exists in the rails not more than about three bore widths behind the armature, the accelerating force is similarly a function of that instantaneous current distribution in the conducting rails right in the vicinity of the armature or driving plasma. Therefore it should be understood that the significant value of L' is the inductance gradient existing in the current conducting rails right behind the armature. Simple parallel rail launchers of the prior art have used rectangular cross section projectile launching rails and designs have been proposed wherein the bore is circular and the rails are then essentially formed from annular sectors. Although such rails have been shown to be practical, substantial projectile acceleration improvements can be obtained by utilizing rail cross sections which result in higher acceleration forces in, for example, the breech area, and other configurations which can be utilized to increase accelerating force where the projectile is already traveling at a high speed and when the accelerating current has been reduced. The present invention utilizes particular rail configurations to achieve acceleration improvements.